Method of operating high pressure oil and gas wells



Jan. 19, 1943. J. L. HILL v 2,309,075

METHOD OF OPERATING HIGH PRESSURE OIL AND GAS WELLS Filed March 9, 1939 .Sepa/afar INVENTOR ATTONEY Patented Jane-19,1943

METHOD F OPERATING UIL AND GAS man rarissima .1 m4 I f .lohn L. mu, palm, rex., me of one-hen to' Continental Oil Company, Ponca (lity, 0h19., a

corporation of Delaware Y application Masch e, 1939, semi No. 260,124

(ci. 16s-21) My invention relates to a method of operating high pressure oil and'gas wells, and more particularly to a, method of recovering liquid hydrocarbons from high pressure wells.

Frequently highy pressure wells are vdrilled where the gas-oil ratios encountered are high, and in which production is economically prohibitive because oi existing State conservation laws. For example, the laws of the State of Texas prohibit the removal of more than 2,000 cubic feet of gas per barrel-` of oil recovered. In order to operate a'well in which the gas-oil ratios are high, it would be me to return gas over 2,?00 cubic feet per barrel of oil recoveredtothevell.

, This necessitates a large capital expenditure for equipment enabling the return of excess gas to the producing stratum under extremely high pressures. 'Since it is necessary to reduce the pressure of the gas-oil mixture removed from the well in order to eect an oil recovery, an expenditure in energy to recomprcss the excess gas to pressures sumcient to enable its return to the producing stratum is required., In a high pressure well, the pressure at which optimum liquid recovery takes place is always considerably below the pressure required to return the gas to the formation from which it was removed. The capital expenditure in the necessary equipment, and the cost of operating the equipment to recompress the gas in order to be able to return it to thedesired point in the formation, renders the production of certain high pressure wells, in which high 'gas-oil ratios exist, commercially impracticable.

In gas-vapor mixtures, the vapor may be re-v moved by'compressing the gas and cooling the compressed gas to form a condensate only between atmospheric pressure and pressures between 500 and '700 pounds per square inch. After this critical pressure is reached, further compression will cause the liquid to redissolve in the compressed gas and it cannot be precipitated i'romL the mixture. It appears that the liquid goes into solution with the compressed gas in increasing amounts if the pressure increases above a point usually between 500 and 700 pounds per square inch. This point is the critical point beyond which it becomes progressively more and more diflicult to distinguish liquid from gas. 'I'he critical phenomenon was discovered by Andrews (Phil. Mag. (4) 39,150 (1870)).

It will be apparent, therefore, that in dealing with high pressure gas-vapor mixtures, in which the pressure is above the critical pressure, liquid recovery must be eilected by a reduction of pressure upon the gas-vapor mixture to within or below the critical pressure range for the temperature. The range at which the liquid constituents precipitate from solution or suspension in the compressed gas is termed the retrograde condensation range. 'I'his range, of course, varies depending upon the particular composition of the liquid. Recovery is increased with a lowering of the temperature. It the pressure is reduced below the critical pressure range, no additional liquid will condense at a given temmrature. Below the retrograde condensation range a further reduction in pressure will result in a redissolution of the vapors in the gas in proportion to their respective vapor pressures and molal concentrations, in accordance with the well mown gas laws.

As pointed out above, the critical phenomenon has long been well known to the art. In operating a high pressure well in which the pressures are above the critical range, to recover normally liquid hydrocarbons, it is necessary (a) To reduce the pressure to below the critical pressure:

(b) To cool the gas-vapor mixture to enable the precipitation of liquid hydrocarbons.

In orderpto comply with the State laws, it is necessary to return all gas in excess of 2,000 cubic feet per barrel of liquid hydrocarbons produced to the formation.

One object of my invention is to provide a method of operating high pressure wells in an economical manner.

Another object of my invention is to provide `a method of operating high pressure wells in which the energy available in expanding the high pressure gas-vapor mixture to below the critical pressure is utilized in not only reducing the.

temperature of the mixture, but also producing work through expansion, which work is employed to recompress previously expanded gas for return to the formation from which it was removed.

Other and further objects of my invention will appear from the following description.

'I'he accompanying drawing, which forms part of the instant specification, and which is to be read in conjunction therewith, is a diagrammatic view of one form of apparatus capable of carrying out the method of my invention.

Referring now to the drawing, a. gas-vapor mixture is taken from a well head I through pipe 2. It is understood that the well is under vided between the well and the after equipment.

In passing through the choke the material taken` from the well will be reduced in reduction in pressure through the choke expends' energy which is not' employed in any useful way. In order to make available theiullof the well in doing useful work, I permit the full Liquid components, such as water or foreign' matter, and entrained oil still liquid at-theformation pressure, are removed from the Separator d through pipe controlled by a liquidlevel controlled valve 6. The gas 'atiliat the 'well pressure is withdrawn from the separator 4 through pipe Ii' the temperature to which the gas will be cooled in the expander cylinder Ais below that at which gas hydrates will form, megas-is d through a dehydrator s before being itted to flow into the expander cylinder t. The dehydrator may be of any suitable time. .Such as a chamber containing silica gel or anyother suitable dehydration material. To the .gas through the dehydrator t, valve I@ isclosedand valves Ii and i2 are opened. If thechilling panded gas containing droplets of precipitated liquid and vapors are passed through pipe Il, through a heat exchanger It, to which refrigerating medium is supplied through pipe Il. The chilled expanded mixture leaves the heat exchanger IB through pipe I8 and passes through .pipe i9 .into a recovery tower. 20, in which the precipitated liquid is separated and .withdrawn through pipe 2|, controlled by noat controlled -valve 22. It will be understood that if the expanded gas is to pass through the heat exchanger l5 well pressure to exist up to the edercylineV der, as will be hereinafter more fully described which ensues in the expander cylinders is not 3'5 below the temperature at which gas hydrates will form, the valves il and i2 are closed and valve IG is opened bypassing the dehydrator 8. The gas passes into the expander cylinder t, through pipe It. It will be understood, of course, that the expander cylinder is shown for the purpose oi' illustration, and not by way of limitation, since any suitable device in'which a gas may be expanded to do work. such as a turbine, may be employed. I! desired, the expansion may be in a plurality of stages, employing a plurality of cylinders successively larger in size. 'Similarly, tandem cylinders may be employed if desired. The expander cylinder servesthree vfunctions, namely,

(a) Acts as a well choke, i

(b) Permits the gas to expand tofcolthe same,

(c) Converts the potential energy ofpressure into work by driving a piston or vother" mechanical device for converting compressed work.

The piston within the expander cylinderwilh be reciprocated in a manner well knolvffn't'the'. art to drive a compressor I@ for v.gas previously separated in the process pti to.

Permit Optimum recovery. In such cases'the'^.^ 75v IB, valve 23 will be closed and valves 24 and 2,5 will be opened. If the heat exchanger is not required, valves 24 and 25 will be closed, and valve 23 will be opened, permitting the gas to pass through pipe 28 into pipe I9 and hence into the recovery tower 20.

A portion of the gas from the recovery tower not exceeding that permitted by the state laws in which the well is situated, may be withdrawn through pipe 21, controlled by back pressure controlled valve 28, for passage through pipe 28, controlled by shut off valve 30, to the fuel gas mains. The bulk of the sas removed from recovery tower 20 passes through pipe 3l to the compressor Iii, in which it is recompressed to slightly above Ithe pressure of theformation to which it is to be returned.

'Ihe compressed gas denuded of normally liquid fractions leaves the compressor through pipe 32, and is returned to the formation either through pipe 33 to the well head l, from which it was Withdrawn, or through pipe 35 to the well head 34 of a repressuring well. It is Well understood in the art that where a plurality of wells communicate with a single formation. sas may be withdrawn from a number oi.' the wells grouped about a repressuring well to which the recompressed gas is charged for passage to the formation.

In some instances where the gas is lean in normally liquid constituents, it may be necessary to use an auxiliary compressor. In such cases. I provide an auxiliary compressor 38, actuated by a prime mover, such as an internal combus- -tion engine 31. 'I'he auxiliary compressor is oonnected in parallel with the main compressor I4. It takes suction through pipe 31 from the pipe 3|. The compressed gas is discharged from the auxiliary compressor 36 through pipe 38 and is psed into the compressed gas pipe 32 along l with the bulk of the recompressed gases leaving the compresso;` I4.

It will be seen that I have accomplished the objects of my invention. I have provided a method of operating a high pressure well in an economical and expeditious manner in order to recover useful liquid hydrocarbons. My method 4enables wells to be operated which could not otherwise be operated because of the cost of re- -icompressing the expanded gas.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further obvious that, various changes may be made in details witlriip the scope of my claims without departing from the spirit of my invention. It is, therefore-sto be understood that my invention is not tobeilimited to the specific details shown and described.

y Having thus described my invention, I claim:

1'.'l A method of operating oil and gas wells to recover desirable liuueiiable hydrocarbons in a asoaovs formation in which the pressure is above the critical pressure, including the steps of expanding the hydrocarbons withdrawn from the well from the formation pressure to a. pressure below the critical pressure and .within the retrograde condensation range, converting pressure energy into kinetic energy during said expanding step, separating precipitated liquid constituents from uncondensed gases in a liquid recovery zone, withdrawing liquids from said recovery zoneas the desired liquid hydrocarbons, withdrawing uncondensed gases from said recovery zone, recompressing said uncondensed gases by means of said kinetic energy, and returning the compressed gases to the formation from which they were withdrawn.

2. A method as in claim 1 in which the hydrocarbons withdrawn from the well are subjected to a separation step at the formation pressure before being passed to said expansion step.

3. A method as in claim 1 in which the hydrocarbons withdrawn from the well are subjected to a dehydration step before being passed to said expansion step.

4. A method as in claim 1 in which the hydrocarbons withdrawn from the expansion step are chilled by heat exchange with a cool external medium before -being passed to said liquid recovery step.

hydrocarbons and a residual gas fraction.

7. The method of recovering liquid hydrocarbons from a fluid produced by a well of the distillate type at a high well head pressure which comprises expanding said fluid from a pressure of the order of said well head pressure to a pressure within the retrograde condensation range while said iuid does work, separating said expanded uid into a, fraction comprising liquid hydrocarbons and a residual gas fraction, utilizing at least a part of the work done by said expanding iiuid to compress at least a part of saicll residual gas fraction, and cycling said recompressed gas to a, subsurface formation.

JOHN L. HILL. 

